Alkanes (unfinished rn)

Question 1

What are the features of methane?

Answer 1

• Forms naturally outside of crude oil
• Forms from anaerobic respiration in the gut of certain mammals (e.g. cows and sheep)
• This also happens in compost heaps, rice fields and landfill waste tips
• Methane is a greenhouse gas

Question 2

Why are alkanes non-polar?

Answer 2

Because there is little/no difference in electronegativity.

Question 3

Why does the melting and boiling points of alkanes increase with chain length?

Answer 3

More van der waals, which take more energy to overcome.

Question 4

Why do branched alkanes (isoalkanes) have lower melting and boiling points than unbranched alkanes with the same molecular mass?

Answer 4

Isoalkanes have less van der waals/intermolecular forces due to a decreased surface area, which take less energy to overcome.

Question 5

Why do alkanes not dissolve in water but do in other alkanes?

Answer 5

Because water’s hydrogen bonds are stronger than the van der waals forces that would occur between an alkane/water.

Question 6

Do alkanes dissolve in other non-polar liquids?

Answer 6

Yes.

Question 7

How do you separate alkanes from a polar solvent?

Answer 7

A separatory funnel.

Question 8

How do you separate alkanes from a non-polar a solvent?

Answer 8

Fractional distillation.

Question 9

How was crude oil formed?

Answer 9

From decomposed small organisms (e.g. plankton) under heat, pressure and no oxygen.

Question 10

What is cracking?

Answer 10

Breaking longer chain alkanes into shorter chain molecules.

Question 11

What are the two types of cracking?

Answer 11

• Thermal cracking
• Catalytic cracking

Question 12

What are the conditions for thermal cracking?

Answer 12

• Very high temperature (1000-1200 kelvin)
• Extremely high pressure (up to 70 atmospheres)
• Produces a high amount of alkenes
• High temperature and pressure is very expensive and can potentially decompose the molecule to produce carbon and hydrogen

Question 13

What are the conditions for catalytic cracking?

Answer 13

• Presence of a zeolite catalyst
• Temperature around 800-1000 kelvin
• Pressure between 1-2 atmospheres
• Tends to make aromatics and motor fuels

Question 14

What is a zeolite catalyst?

Answer 14

It is made from aluminium oxide and silicon dioxide and has a honeycomb structure (this increased surface area increases rate of reaction).

Question 15

What is complete combustion?

Answer 15

Burning something in a sufficient supply of oxygen.

Question 16

What is incomplete combustion?

Answer 16

Burning something in the presence of an insufficient supply of oxygen.